1. Field of the Invention
The present invention pertains to a gauge for measuring the thickness of a coating applied to a surface and, more particularly, to a hand-held gauge for measuring the thickness of a coating applied to a metal surface which visually signals to the user the appropriate time at which to read a thickness gauge.
2. Background of the Invention
Various devices for measuring the thickness of a coating applied to a surface are known in the art as represented by U.S. Pat. Nos. 3,462,848, 4,567,436, 4,715,007 and 4,912,410. Each of these known gauge arrangements are particularly adapted to measure the thicknesses of coatings applied to metal surfaces in a manner similar to the present invention, but due to their construction and/or operation, they tend to be inaccurate, rather expensive to produce and/or not readily transportable.
For example, the gauge in U.S. Pat. No. 3,462,848 requires a base of a hand-held gauge body to be maintained in contact with the surface upon which the coating, whose thickness is to be measured, is applied while a cutter member is rotated. Maintaining the base of the gauge body in engagement is seen to be difficult due to the manner is which the gauge body can be grasped and the fact that the base is angled relative to the surface. Due to this angled base arrangement, when the cutter member is rotated, an arcuate groove, that increases in depth, will be placed in the surface. When the cutter member fully penetrates the coating and comes into contact with the metal surface, an electrical circuit will be completed and a light will illuminate to indicate to the user that the thickness of the coating can be read from a dial. Due to this measurement arrangement, not only is an undesirable groove placed in the surface, but the gauge cannot accurately read the coating thickness to a great degree of accuracy as the base can easily come out of engagement with the surface.
The thickness measuring gauge disclosed in U.S. Pat. No. 4,567,436, utilizes a magnetic sensing arrangement to determine the thickness of a coating applied to a metal surface. Although this gauge arrangement can be adequately positioned and supported on the surface to enable accurate readings, there exist numerous factors that can easily alter the accuracy of the unit and which significantly increase its cost. For instance, the magnetic field must be properly aligned by a set screw, the magnetic material must be manufactured to rather high purity levels, a balancing arm, which carries a magnetic thickness gauge, must be dynamically balanced and then the actual visual gauge must be calibrated using plates provided with various different known coating thicknesses. Due to the difficulty in calibrating this gauge, it is hard to justify transporting the unit for fear of a loss of accuracy.
U.S. Pat. No. 4,715,007 discloses an electromagnetic coating thickness sensing device wherein a probe is placed in contact with the coated surface and a generated electromagnetic field is sensed and converted to a coating thickness value. Although this device advantageously does not require any portion of the coating to be removed in order to measure its thickness, this arrangement does requires sophisticated electrical circuitry and components which undesirably add to the cost of the device.
Finally, the apparatus for measuring the thickness of an electrically nonconductive material on a metallic based disclosed in U.S. Pat. No. 4.912.410 utilizes an electrical measuring coil that is adapted to be supported over the surface by means of a constant pressure source of air supplied by nozzles. An electrical response is produced in the measuring coil from the metal which is dependent upon the distance which the measuring coil is maintained above the surface by the air pressure. This distance will depend on the thickness of the coating. Due to the construction of this system, the device is not readily transportable, is considered unduly complicated, and is rather expensive to manufacture and operate.
Therefore, there exists a need in the art for a coating thickness measuring device which is relatively inexpensive to manufacture, readily transportable, accurate and which does not unduly mar or damage the coating during use.